This invention pertains to metal surface treatment wherein an aqueous acidic solution of hydrogen peroxide is used. More specifically, the invention relates to the use of particular stabilizers to retard the decomposition of the hydrogen peroxide which normally is encountered when using such solutions to treat metal surfaces.
When a metal substrate is processed, a metal oxide layer often forms on the substrate surface which adversely affects the surface appearance and/or the ability to carry out further desired processing steps. It is therefore desirable to remove or at least reduce the amount of the metal oxide coating on the substrate surface. These processes are generally referred to in the field as metal pickling, metal polishing, or metal brightening, depending upon the particular type of surface treatment being used.
Solutions of hydrogen peroxide, and in particular aqueous acidic solutions of hydrogen peroxide, are commonly used in industry to clean or otherwise treat metal surfaces. However, during the course of such treatment, metal ions originating from the metal oxide layer typically accumulate in the solution. For economic reasons, it is standard practice to avoid discarding metal treatment solutions frequently, so that over time the concentration of metal in solution tends to increase. Many metals will catalyze hydrogen peroxide decomposition, especially when the solution is acidic. As the hydrogen peroxide concentration decreases, the efficacy of the treatment solution is reduced and additional hydrogen peroxide must be added to restore the treatment solution performance. If a relatively high rate of hydrogen peroxide replenishment is needed due to rapid decomposition, the economics of the metal treatment process become much less favorable.
The invention pertains to a stabilizer composition useful for stabilizing an acidic aqueous solution of hydrogen peroxide, said stabilizer composition comprising an aryl sulfonic acid or salt thereof (preferably, a hydroxy-aryl sulfonic acid or salt thereof, most preferably, phenol sulfonic acid or salt thereof) and a triazole or salt thereof (preferably, a benzotriazole or salt thereof, most preferably, tolyltriazole or salt thereof). The water-soluble salts of aryl sulfonic acids and triazoles (especially the alkali metal salts) are particularly preferred for use when the stabilizer composition is in concentrate form (i.e., before being combined with the mineral acid component of the acidic aqueous solution).
Additionally, the present invention provides a hydrogen peroxide solution stabilized against decomposition catalyzed by metal ions, said solution comprising water, hydrogen peroxide, an aryl sulfonic acid or salt thereof and a triazole or salt thereof.
The invention further pertains to a process for treating a surface of a metal substrate, said process comprising:
a) contacting said surface with an aqueous acidic solution comprised of water, hydrogen peroxide, a mineral acid, an aryl sulfonic acid, and a triazole; and
b) maintaining said surface in contact with said solution until at least a portion of said metal oxide layer has been removed from said surface.